The object of the proposed research is to discover the behavioral contributions of tectal, thalamic and cortical auditory centers to mammalian hearing. The overall strategy combines anatomical and behavioral techniques in a two-fold organ level analysis of central auditory mechanisms. First, standard anatomical techniques such as Nissl, Golgi and Fink-Heimer procedures will be employed to determine homologous auditory structures on the basis of architectonics and neuronal connections. Once the homologous structures are known the ablation-behavior technique can then be used to determine the unique contributions of tectum, thalamus and cortex to hearing. The significance of the proposed research for human health is two-fold. The first is the close similarity between surgical destruction of brain tissue and damage caused by neurological disorders such as stroke. The second is the more fundamental idea that the greater our knowledge of the nervous system and how it evolved, the greater our capacity will be to understand human brain disorders.